Microbiology: Microbes, Domains, and Identification

• A microbe is a microscopic organism, including bacteria, viruses, fungi, protists, and archaea.
• The three domains of life include Bacteria, Archaea, and Eukarya.

Viruses

• Non-living entities that require a host cell to replicate.
• Contain either DNA or RNA as their genetic material.
• Possess a protein coat called a capsid.

Bacteria

• Archaebacteria thrive in extreme environments, while Eubacteria are found in more common conditions.

Microbial Identification

• Methods include:
  • Phenotype (morphology, staining)
  • Genetics (PCR, sequencing)
  • Serology
  • Phage testing
  • Bergey’s Manual
• Approximately 99% of microbes are beneficial, while only about 1% are pathogenic.
• Tuberculosis is the leading infectious disease killer worldwide.
• COVID-19 became a leading cause of infectious disease deaths during the pandemic.
• Major historical epidemics include the Black Death, Smallpox, Cholera, Influenza, AIDS, and COVID-19.
• Epidemic occurrences have been reduced by vaccination, sanitation, antibiotics, and public health measures.
• Louis Pasteur disproved spontaneous generation through the swan-neck flask experiment.

Cell Theory

• All living things are composed of cells.
• Cells arise from pre-existing cells.
• Robert Koch proposed the Germ Theory of Disease.
• Joseph Lister introduced antiseptic techniques in surgery.
• Edward Jenner developed the first vaccine (smallpox).
• Alexander Fleming discovered penicillin, the first antibiotic.
• An etiological agent is the pathogen that causes a disease.
• Contamination refers to the presence of microbes, while infection is when microbes grow in the host.

Koch’s Postulates

• Isolate the pathogen.
• Grow it in pure culture.
• Introduce it to a healthy host.
• Re-isolate the pathogen.
• Koch’s Postulates might not always work because some microbes cannot be cultured or some diseases have multiple causes.
• A reservoir of infection is the natural habitat where a pathogen lives, such as humans, animals, or non-living sources.
• Zoonotic diseases include rabies, Lyme disease, and plague.

Types of Disease Transmission

• Contact (direct, indirect, droplet)
• Vehicle (water, food, air)
• Vector (mechanical, biological)

Vector Transmission Examples

• Mechanical: A fly carrying bacteria.
• Biological: A mosquito transmitting malaria.
• An opportunistic infection occurs when the immune system is weakened.

Cell Differences

• Prokaryotic cells:
  • Lack a nucleus
  • Are smaller
  • Have circular DNA
  • Possess 70S ribosomes
• Eukaryotic cells:
  • Have a nucleus
  • Are larger
  • Have linear DNA
  • Possess 80S ribosomes
• Bacterial flagella function in motility (movement).
• A glycocalyx is a protective outer layer that can be a capsule (tight) or slime layer (loose).

Gram Differences

• Gram-positive bacteria:
  • Have thick peptidoglycan layers
  • Stain purple
• Gram-negative bacteria:
  • Have thin peptidoglycan layers
  • Have an outer membrane
  • Stain pink
• Endospores allow bacteria to survive harsh conditions.

Biological Molecules

• The four main types are carbohydrates, proteins, lipids, and nucleic acids.
• Dehydration synthesis is a reaction where monomers combine, releasing water.
• Hydrolysis is a reaction where polymers break down, requiring water.
• An enzyme is a protein that speeds up chemical reactions.
• NAD+ and FAD are electron carriers in cellular respiration.

Aerobic Respiration Stages

• Glycolysis
• Krebs Cycle
• Electron Transport Chain
• Oxygen is the final electron acceptor in aerobic respiration.
• Nitrate and sulfate are final electron acceptors in anaerobic respiration.
• Fermentation is energy production without oxygen, producing lactic acid or ethanol.
• ID50 is the infectious dose that causes disease in 50% of hosts.
• LD50 is the lethal dose that kills 50% of hosts.

Stages of Disease Development

• Incubation
• Prodromal
• Illness
• Decline
• Convalescence

Infections

• Acute infections: Rapid onset, short duration.
• Chronic infections: Slow progression, long-lasting.
• Local infection: Skin infection.
• Systemic infection: Blood infection (sepsis).
• Top three types of nosocomial (hospital-acquired) infections are UTIs, pneumonia, and surgical site infections.
• An Epi-Curve shows the number of cases of disease over time.
• The CDC (Centers for Disease Control and Prevention) monitors disease outbreaks.
• Notifiable diseases include tuberculosis, COVID-19, and measles.
• Reemerging diseases include measles and drug-resistant TB.
• Mutations contribute to new pathogens by creating new strains, affecting virulence and resistance.